Tensioners for flexible drives, such as accessory serpentine belts on automotive engines are well known. Such tensioners typically include a pulley, roller or other member, which is biased against the flexible drive by a spring or other biasing means. The pulley is mounted, via a bearing, to an arm which pivots with respect to the tensioner housing. The housing contains the spring or other biasing means which biases the arm towards the flexible drive to maintain a substantially constant tension in the flexible drive. Tensioners can also include frictional members which ride on one another as the tensioner arm moves to provide a dampening force to the tensioner.
While such prior art tensioners are widely employed, they do suffer from some disadvantages. In particular, due to the relatively large forces which must be carried by the tensioner arm, the spring, or other biasing means, and/or frictional dampening members must be sized to be relatively robust and the resulting large size (i.e.—the “packaging volume”) of the tensioner increases the height (the distance between the mounting plate of the tensioner and the mid point width of the pulley or roller) of the tensioner.
While in some circumstances the relatively large height of the tensioner is not a problem, in many other circumstances it is a factor as the volume of the engine compartment in which the engine and tensioner are to be located can be quite small. In the past, this issue has resulted in the tensioner being located in a less than ideal position on the engine and/or the tensioner components being downsized, to occupy less volume, at the cost of reduced robustness.
It is desired to have a tensioner which has the desired dampening characteristics and robustness while requiring less height for mounting.